Around liberal Twitter, it was a total game changer. “THIS
IS BIG!!!!!!” typed Amy Siskind of New Agenda, hailing the sort of
news for which four or five exclamation points won’t do.
“What’s Russian for ‘Trump’s goose is
cooked?’ ” crowed Harvard’s Laurence Tribe.

In the opposite camp, the Trumpian claque at Breitbart argued
that with the combative New York AG on board — Schneiderman
has long feuded with Trump, and is widely disliked by Republicans
— the whole Russian probe can be dismissed as tainted. The
connection “undermin[es] the integrity and impartiality of
Mueller’s inquiry,” wrote Joel Pollak. “There could not be a
more inappropriate person to be seen working with
Mueller.”

It could hardly be
otherwise under our two-level system of prosecution, under which
patterns of misbehavior can readily generate both federal and state
offenses.

Both sides should calm down. Yes, the cooperation between the
feds and New York is an important side of the story. What’s
absent is a real indication that much new or unusual is afoot.

Federal and state prosecutors are supposed to cooperate when
investigations overlap. That’s what they do. From the little
that has been pinned down so far, it’s hard to see that
they’re cooperating in any way they wouldn’t be if
persons other than Mueller and Schneiderman were in charge.

It’d be one thing had Mueller gone shopping for help to
some state with little connection to the Russian affair. But as the
locus of the Trump organization and campaign, New York is at the
center of the probe, even if other states have connections,
too.

We know that the Trump Tower meeting attended by Donald Trump
Jr. is a focus of the probe because Rinat Akhmetshin, one of its
participants, spent hours recently testifying before
Mueller’s grand jury.

It could hardly be otherwise under our two-level system of
prosecution, under which patterns of misbehavior can readily
generate both federal and state offenses. Conversely, state law
enforcers looking into violations of state law may come upon
evidence that federal law has been broken, and they, too, routinely
share such information with their federal counterparts.

The US attorneys’ handbook, which Mueller would be
expected to follow, provides expressly for sharing federal
grand-jury evidence with state and local law enforcement when it
points to such crimes. Were Mueller to step down or be fired
tomorrow, his successor would be called on to “team up”
with state counterparts in this same way.

Let’s review the bidding. In the aftermath of
Trump’s pardon of Arizona sheriff Joe Arpaio following a
federal contempt conviction — which sent ripples of dismay
deep into Republican legal circles — a lot of us are looking
for reassurance that the chief executive can’t pardon every
offense his backers might commit.

And that reassurance is right there in the Constitution, which
makes plain that the president has no power to pardon crimes under
state law. Nor can he fire state law-enforcement officials like
Schneiderman.

It’s believed that part of the Paul Manafort probe
(in which Manafort denies all wrongdoing)
involves possible violations of money-laundering laws, and other
financial charges may surface. Under New York’s unique Martin
Act, its attorney general wields unique financial investigatory
powers.

As I wrote for these pages in 2011, the Martin Act is a virtual
“blank check for the prosecution” that gives New
York’s AG “super-broad powers to investigate and press
charges against alleged financial fraud.” In particular, he
can “subpoena witnesses or demand the production of documents
without probable cause or a grand jury’s say-so.” He
can also leak things he finds, or keep them private, as suits his
whim.

These powers go too far and should be rolled back, but the
Schneiderman-Mueller cooperation appears to fall squarely within
them.